This proposal seeks competitive renewal of my GM049369, which has been supporting our basic research in regulated gene expression by RNA binding proteins (RBPs) in the past two decades. We will focus on two families of RBPs, SR proteins and RBFoxs, which have been best characterized for their functions in regulated pre-mRNA splicing. However, our recent studies show that they are also directly involved in transcriptional control through interacting with regulatory RNAs in mammalian cells. Built on these paradigm-shifting discoveries, we propose to test a series of hypotheses by pursuing three specific aims. The first is to elucidate synergistic interactions of SR proteins in the cell to test the hypothesis that SR proteins are engaged in network interactions to establish their specificity in interacting with cis-acting RNA elements in mammalian genomes. The second aim to pursue the newly established function of SR proteins in transcriptional control. We are particularly interested in testing the idea that SR proteins are directly involved in the regulation of transcription bubbles at gene promoters to gauge the levels of gene expression. The third aim is to dissect the mechanism for RBFox2 to regulate global targeting of the polycomb complex. The grand hypothesis we will test is that RBPs are broadly involved in transcriptional control through interacting with diverse regulatory RNAs in mammalian genomes. As all genes we are studying have been tightly linked to various human diseases, particularly cancer, the proposed research will not only elucidate new regulatory paradigms, but also provide the theoretical foundation for developing new therapeutics against specific human diseases.